The present invention relates to mine roof support systems, and the like, and more specifically to the class of mine roof supports wherein a bolt carrying a bearing support plate is anchored in a bore hole by both a resin grouting and mechanical expansion anchor.
Two means which have been commonly used for many years to anchor elongated members in drill holes for the purpose of supporting and reinforcing the rock strata of mine roofs are chemical grouting and mechanical expansion anchors. Each of these systems had its own advantages and drawbacks, one of the early disadvantages of an anchorage provided solely by a chemical or other grouting being that the bolt or rod could not be tensioned by threading into a nut, or the like, within the bore hole to compress the rock strata between the bearing plate and inner end of the bore hole. This problem was overcome by the anchor system disclosed in Hill U.S. Pat. No. 3,877,235, which provided a resin grouted anchor which could also be tensioned by rotation of a threaded bolt after the resin had set sufficiently to hole a portion of the anchor as excess torque was applied to the bolt to break a stop means.
Anchoring systems both before and after the Hill patent utilized both resin grouting and mechanical expansion anchors in roof support systems utilizing various means for mixing the components of a two-part resin system. For example, in Dempsey U.S. Pat. No. 2,952,129 the components were mixed manually in a breakable container just before being placed in the bore hole; Schuermann et al U.S. Pat. No. 3,188,815 employed an expansion anchor which traveled down the threads as the bolt was rotated to mix the resin components, whereby expansion of the anchor upon reaching the bottom of the threads was delayed until mixing was complete; in Clark, et al U.S. Pat. No. 4,162,133 a two-compartment resin package was broken and the contents mixed by reverse spin of a bolt and expansion anchor, followed by forward spin to set the anchor; Callandra U.S. Pat. Nos. 4,413,930, 4,419,805, 4,516,885, and 4,518,292 all rely upon breaking a stop means by application of excess torque to the bolt, as in the Hill Patent, to expand the anchor after the resin has set sufficiently to resist continued rotation of the expansion anchor together with the bolt; White et al U.S. Pat. Nos. 4,483,645, 4,534,679 and 4,534,680 provide various means to delay expansion of the expansible portion of the anchor until after a predetermined number of revolutions of the threaded rod, normally a length of steel rebar having protrussions on the exterior surface to aid in the mixing process.
In recent years, improvements in the components and packaging of resin cartridges used in mine roof support applications have resulted in a significant decrease in the amount of time required for mixing of the resin and catalyst by rotation of a bolt, or other such member, within a bore hole. In fact, mixing time has been reduced to the point that it is no longer necessary to delay the opening of an expansion anchor used in combination with the resin to provide a tensioned roof bolt anchorage. Conventional expansion anchors are fully engaged and the bolt tensioned after about 3 to 5 seconds of rotation, which is sufficient to provide adequate mixing of the resin and catalyst, particularly when rebar having an embossed pattern on its outer surface is used in place of a smooth bolt. Thus, roof support systems are currently in use which include a two-compartment resin cartridge and a rebar carrying a standard expansion anchor on a threaded end portion thereof.
It is a principal object of the present invention to provide a mine roof anchor system including both resin grouting and a mechanical expansion anchor wherein the components of a two-compartment resin package are mixed in an improved manner as the anchor is set by rotation of the bolt on which it is carried.
A further object is to provide a combined resin-mechanical mine roof support system having superior anchoring capabilities with economy of components.
Another object is to provide an improved resin-mechanical anchoring system which may be installed rapidly, requiring no more time than installation of a standard expansion anchor.
Still another object is to provide a mine roof anchor system wherein a two-compartment resin package is inserted into a drill hole ahead of a threaded rod carrying a conventional, mechanical expansion anchor, and the resin components are mixed to provide a secure chemical anchor as the rod is rotated to set the mechanical anchor in the standard manner using only the number of revolutions needed to expand the shell of the anchor.
Other objects will in part be obvious and will in part appear hereinafter.